Methods of coating surfaces and in elements comprising such surfaces

ABSTRACT

THE INNER SURFACE OF A LIGHT ALLOY CRANK-CASE ENVELOPE OF A ROTARY PISTON ENGINE IS COATED BY SPRAYING A WEARRESISTANT LAYER THEREON. CARBON STEEL AND NICKEL ALUMINIDE ARE SPRAYED ON SIMULTANEOUSLY BY AT LEAST TWO OXY-ACETYLENE FLAME OR PLASMA FLAME GUNS. SPHERICAL GRAIN PARTICLES SUCH AS SIC, TIB OR BC CAN BE INCORPORTED.

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Y. A. ROSSEAU 3,674,544

METHOD- OF COAT SURFACES AND IN ELEMENTS OMPR ISING SUCH SURFACES Filed Dec. 24, 1969 INVENTOR BY JMM $5 ATTORNEY United States Patent Int. 01.11051) 5700, 7/08, 7/14 U.S. Cl. 117-93.1 PF 9 Claims ABSTRACT OF THE DISCLOSURE The inner surface of a light alloy crank-case envelope of a rotary piston engine is coated by spraying a wearresistant layer thereon. Carbon steel and nickel aluminide are sprayed on simultaneously by at least two oxy-acetylene flame or plasma flame guns. Spherical grain particles such as SiC, TiB or BC can be incorporated.

The present invention relates to improvements in methods of coating surfaces and in elements comprising such surfaces. More particularly, because it is in this case that its application seems to offer most advantages, but not exclusively, among these elements, it relates to crank-casing envelopes or stators of aluminium-based light alloy for rotary piston engines.

In the operation of a rotary piston engine, the piston rubs along a narrow contact zone thereby exerting a high pressure against the inner surface of the crank-casing. It is already known to apply, on this surface, coatings constituted by materials which improve the friction and possess good resistance to wear, and which are applied to the surface by methods known as metallisation.

It is a particular object of the invention, to provide such methods and elements that respond better than hitherto to the various requirements of practice, especially as regards resistance to wear of the rubbing surface and reduction in the coefficient of friction of the member, such as a piston, which co-operates with the above-said element.

According to the invention, a process for coating rubbing surfaces, especially inner surfaces of crank-case envelopes for rotary piston engines constituted of light alloy, comprises projecting onto the said surfaces, simultaneously, by means of at least two oxy-acetylene flame or plasma flame guns, on one hand, carbon steel and, on the other hand, nickel and aluminium forming, by combination with the oxygen supplied by gun, a composite material comprising nickel aluminides and oxides with substantially ellipsoidal grains, the said composite material, which can also be made to contain, by incorporation on the projection, of spherical grain particles such as silicon carbide and/or titanium boride and/or boron carbide, being alloyed with the carbon steel to form a wear resistant layer, favourable to sliding and averaging a certain minimal thickness, resisting well the high contact pressures developed, according to the method of production preferred, during the operation of the engine,

- which properties, by reason of the nature of the projected materials, are preserved at the operating temperatures of the engine.

According to another aspect of the invention, there is provided an element with a rubbing surface, said element being arranged so that the said surface is covered with a wear resistant layer constituted by an alloy of carbon steel and a composite material formed principally of nickel aluminides NiAl and Ni Al which occur in substantially equal parts with, in smaller proportions, oxides with substantially ellipsoidal grains NiO, A1 0 and NiA1 O which are formed by reaction during the operation and with which may advantageously be incorporated,

3,674,544 Patented July 4, 1972 in smaller proportion, particles with spherical grains, such as silicon carbide SiC and/ or titanium boride TiB and/or boron carbide BC, the wear resistant layer having a thickness advantageously at least equal to 0.3 mm.

Preferably, content of carbon steel is comprised between 0.4% and 1.2% by weight and the proportions, by volume, of the materials to be alloyed may vary from 10% to for carbon steel and from 90% to 10% for the complementary part in which aluminium and nickel are of substantially equal amounts.

Preferably again, the steel is about 0.6% carbon and the proportions, by volume, of the materials to be alloyed are in the neighbourhood of 60% for steel with about 0.6% carbon and 40% for the complementary part in which aluminium and nickel are in substantially equal amounts.

Preferably again, the proportions by volume of the materials to be alloyed are around 60% for steel with about 0.6% carbon and 40% for the complementary part breaking down to 35 to 38% in which aluminium and nickel are in substantially equal amounts and 5% to 2% constituted by spherical grain particles of diameter from 1 to 3p (microns), of silicon carbide SiC, and/ or titanium boride TiB and/or boron carbide BC.

The invention consists, apart from these principal features, in certain other features which are preferably incorporated at the same time and which will be more explicitly described below.

In order that the invention may be more fully under stood, a preferred embodiment of the method according to the invention is described below purely by way of iilustrative and non-limiting example, with reference to the accompanying drawing, in which the single figure shows, in transverse section, a crank-casing produced according to the invention.

According to the invention, a crank-casing 1 of light alloy based on aluminium obtained by moulding or forging, of cylindrical inner shape and of which a perpendicular cross-section has a shape in the form of a trochoid with two arcs, a wear resistant coating is produced on the inner surface 2 of the envelope 1, in the following manner.

According to the invention, there is projected onto the inner surface 2 of the envelope 1, simultaneously, by means of two oxy-acetylene flame or plasma flame guns, on one hand, carbon steel and, on the other hand, nickel and aluminium forming, by combination with the oxygen supplied by the gun, a composite material comprising nickel aluminide NiAl and Ni Al and oxides with substantially ellipsoidal grains, NiO, A1 0 and NiAl O the said composite material and the carbon steel being thus alloyed to form a wear resistant layer 3.

The inner surface 2 is previously machined to dimensions in the neighbourhood of (but slightly greater than) those of the surface 4 which must be obtained for the finished casing 1. The two surfaces 2 and 4 are substantially parallel and their mutual distance 5 is equal to the desired thickness for the wear resistant layer.

To prepare the surface 2 for spraying with fused metal (or metallisation) and to facilitate the attachment of the metallic layer sprayed onto the surface 2, it is advantageous to effect a sanding operation in which there is projected violently against the said surface an abrasive jet, for example of corundum, so as to render the surface 2 rugged and adapted to ensure good adhesion.

The envelope 1 is then brought to a temperature of about C. so as to produce, as explained below, a final prestressing.

The metallisation proper is then carried out by means of two guns adjusted to spray on the same spot, respectively, carbon steel, on one hand, and aluminium and nickel, on the other hand, the materials being supplied to the guns in the form of wire and/or powder. The discharge rates of the guns are adjustable and means are provided to ensure relative rotational and translational movements between the envelope and the assembly of guns so that the whole surface 2 passes before the guns and can be metallised.

A first passage is advantageously effected during which only the aluminium and nickel gun discharges, so as to deposit a thin keying film of composite material formed of aluminides of nickel and of oxides (of thickness generally comprised between 0.02 and 0.05 mm.), over the whole of the surface 2.

The two guns are then simultaneously discharged to form the wear resistant layer proper whose attachment is improved by the above-said thin film. The ratio of the discharges by volume of the two guns is equal to the ratio of the proportions by volume desired for the carbon steel, aluminium and nickel, if desired supplemented with particles of other material.

These proportions by volume may vary between 10% and 90% of carbon steel of which the content of carbon is between 0.4% and 1.2% by weight. Complementarily, the proportion to be followed for aluminium and nickel may vary between 90% and 10%, the aluminium and the nickel occurring in substantially equal amounts. Pref erably, a steel with 0.6% approximately of carbon is selected and a proportion, by volume, in the region of 60% of steel for 40% of complementary part in which aluminium and nickel are in substantially equal amounts. Preferably again, the proportions, by volume of the materials to be alloyed are in the neighbourhood. of 60% steel with about 0.6% carbon and 40% of complementary part comprising 35% to 38% of which aluminium and nickel are in substantially equal amounts and to 2% of particles, with spherical grains of diameter of 1 to 3 4 (microns or thousandths of a millimeter), of silicon carbide SiC, and/or titanium boride TiB and/ or boron carbide BC.

The two guns are made to discharge during as many passes as is necessary to obtain a layer 3 of thickness at least equal to 0.3 mm. This thickness confers on the said layer good resistance to contact pressures exerted by the piston.

The wear resistant layer thus obtained is uniform and has a fine surface porosity which may be put to profit for hot impregnation, in an oven, of the said layer with lubricating products such as, for example, mixtures of graphite and boron nitrite, of tungsten bisulphide and/or of molybdenum bisulphide. Clogging of the pores is thus ensured by products favourable to sliding of the piston.

The envelope 1 is then allowed to cool to ambient temperature, which has the effect of placing under compression the layer 3 which has been deposited on the previously heated envelope 1, hence expanded. A pre-stressing is thus created in the layer 3 of which the mechanical holding will be better on operation of the engine, the temperature of preliminary heating being adapted to the temperature of this operation.

The layer 3 is subjected to a truing operation and, finally to an operation of grinding and/or of rolling for finishing of the geometry and of the surfacecondition.

It has been experimentally observed that the wear resistant layer 3 thus obtained with an alloy ofcarbon steel, of aluminium and nickel if necessary supplemented with particles, and more particularly with the alloy corresponding to the preferred composition, not only resisted wear remarkably but was favourable to sliding on itself of the piston or, more exactly, of the segments, constituted prefera'bly of grey pig iron, of the said piston.

As one hand, the projection of the wear resistant layer 3 is effected very rapilly and, on the other hand, the materials used are relatively cheap in comparison with other materials tried and which gave worse results, the method of coating and the envelope obtained by the invention have been found to be very economical.

Consequently, there is obtained a coating of the inner surface of the crank-case envelope for a rotary piston engine which well meets the desired object.

As goes without saying, and as results besides already from the preceding description, the invention is in no way limited to those of its modes of application, nor to those of is methods of production of its various parts, which have been more particularly envisaged; it embraces, on the contrary, all variations.

What I claim is:

1. A method of forming a coating on a rotary piston engine element constituted of light alloy, comprising projecting on the surface of said light alloy element, simultaneously, by means of at least two flame guns, carbon steel from one said gun, and, nickel and aluminum from another said gun, forming, by combination with oxygen supplied by the gun, a composite material comprising nickel aluminides and oxides with substantially ellipsoidal grains, said composite material alloying with the carbon steel to form said coating.

2. A method according to claim 1, wherein the carbon steel has a carbon content comprised between 0.4% and 1.2% by weight and the proportions, by volume, of the materials to be alloyed are comprised between 10% and of the carbon steel and, complementarily, between 90% and 10% of an addition composed of aluminium and of nickel in equal parts.

3. Method according to claim 2, wherein the carbon steel has a carbon content equal to about 0.6% by weight and the proportions, by volume, of the materials to be alloyed are substantially equal to 60% of carbon steel and 40% of complementary part in which the aluminum and the nickel are in substantially equal amounts.

4. A method according to claim 3, wherein the complementary part is composed, with respect to the total volume,

of the materials to be alloyed, of 35% to 38% constituted by the aluminum and nickel in substantially equal amounts and from 5% to 2% of particles, with spherical grains of diameter from 1 to 3 said particles being composed of at least one of the substances silicon carbide, titanium boride and boron carbide.

5. A method according to claim 1, including bringing the element to a temperature in the vicinity of C. at the: moment of the projection, and cooling so as to cause prestressing, in said wear resistant layer.

6. A method according to claim 1, including depositing before the wear resistant layer, a thin film of composite material, formed of aluminides of nickel and of oxides, to improve the keying of the wear resistant layer.

7. A method according to claim 6, comprising causing tfihe gun producing said composite material to discharge 8. A method according to claim 1, wherein at least one of said flame guns is of the oxy-acetylene type.

9. A method according to claim 1, wherein at least one of said flame guns is of the plasma type.

References Cited UNITED STATES PATENTS 3,413,136 11/1968 Emanuelson et a1.

l17--83.l PF SX 3,481,715 12/1969 Whalen et al. 1l79'3.1 PF SX ALFRED L. LEAVIIT, Primary Examiner K. P. GLYNN, Assistant Examiner U.S. Cl. X.R.

117-93.1 R, 105, 105.2; 2l9-76, 121 P 

